var imglist = document.getElementById("imglist");
console.log(imglist);
var left = 0;
function run(){
    if(left <= -2400){
        left = 0;
    }else{
        left -= 600;
        imglist.style.marginLeft = left + "px";
    }
}
var n = (left % 600 == 0)? n = 2000: n=1000;
var timer = setInterval(run,n);